protoxide

POS

Noun

HYPHEN

pro=tox=ide

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CIDE DICTIONARY

protoxide, n. [Proto- + oxide: cf. F. protoxide.].

That one of a series of oxides having the lowest proportion of oxygen. See Proto-, 2 (b). [1913 Webster]

protoxide of nitrogen, laughing gas, now called hyponitrous oxide<--, used as an anaesthetic in dentistry; now (1950-1996) called nitrous oxide, NO -->. See under Laughing.